Police have reinforced that drivers should not leave their vehicles unlocked overnight, even if they live in a rural area.
The warning follows a case on the night of June 4 on Campion Way, Witham, where a purse containing bank cards, a driving licence and £50 in cash was stolen from an unlocked Smart car.
Sergeant Martin Richards of Witham Police said: "Around ten per cent of cars are left open in urban areas and this figure rises to around twenty per cent in rural places.
"People do go around trying car doors and this means that as many as two in ten cars will be vulnerable."
He said drivers should never leave their cars unsecured or leave any property on display.
If you have any information about the theft on Campion Way, call police on 101.